Trichloroethylene stabilized with propargyl alcohol and pyrrole



United States Patent TRICHLOROETHYLENE STABILIZED WITH PRO- PARGYLALCOHOL AND PYRROLE Gordon G. Willis, Lake Jackson, and Claiborne A.

Christian, Freeport, Tex., assignors to The Dow Chemical Company,Midland, Mich., a corporation of Delaware No Drawing. Application April20, 1954, Serial No. 424,495

Claims. (Cl. 260-6525) This invention relates to a composition of mattercomprising trichloroethylene and an inhibitor mixture to prevent it fromdecomposing and attacking metals.

Trichloroethylene (CHCl:CClz) is used in industry mainly as a solventfor cleaning metal articles, especially by the vapor-degreasing process.In this service, it may come into contact at elevated temperature withmost of the common metals, and also with lubricants, sulfurized cuttingoils, bufling compounds, and other agents used in metal working. Underthese severe conditions, the normal slight decomposition oftrichloroethylene when in contact with metal, particularly when moistureis present, is greatly increased. The trichloroethylene may discolorbadly over a period of weeks and also develop acidity suflicient toattack reactive metals such as aluminum and non.

To olfset this behavior, it is conventional to add to thetrichloroethylene one or more inhibiting agents, usually unsaturatedhydrocarbons or organic nitrogen bases. Many of these agents are ofconsiderable help, but none used heretofore has been more than partlyeffective.

It is therefore the principal object of this invention to provide aninhibiting composition which is far more effective in stabilizingtrichloroethylene during storage, shipment, and use than any heretoforeemployed.

The inhibiting compositions of the invention consist essentially of alower acetylenic alcohol and a lesser but substantial proportion of apyrrole having less than 8 carbon atoms per molecule. Further advantageis realized by also including a minor but appreciable proportion of anorganic nitrogen base having a substantial vapor pressure at the boilingtemperature of trichloroethylene. A minor proportion of the inhibitingcomposition, usually less than one percent, is dissolved in thetrichloroethylene to be stabilized.

In the new compositions, the lower acetylenic alcohol is one containingless than six carbon atoms per molecule. Propargyl alcohol is preferredboth because of its more ready availability and, for some conditions,greater elfectiveness. However, any of the other lower acetylenicalcohols may be used, e. g. butyn-1-o1-3 (methyl ethinyl carbinol),butyn-2-ol-l (propinyl carbinol), and methyl- 3-butyn-1-ol-3 (dimethylethinyl carbinol). The propor tion of propargyl alcohol, or otheracetylenic alcohol, required in stabilizing trichloroethylene accordingto the invention is in general from about 0.005 to 1.0 percent,preferably 0.05 to 0.5 percent (all proportions given herein are byweight).

In addition to the acetylenic alcohol, the new inhibiting compositionscontain a pyrrole having less than 8 carbon atoms per molecule. The terma pyrrole as used herein means pyrrole itself and homologs of pyrrole,containing the pyrrole nucleus.

Pyrrole itself is entirely satisfactory and is usually preferred.However, homologs such as the N-lower alkyl pyrroles, e. g. N-methylpyrrole and N-ethyl pyrrole, and such as Z-methyl pyrrole, 2,5-dimethylpyrrole, may also be employed. The proportion of pyrrole or pyr- ICC 2role homolog needed for stabilizing trichloroethylene is in general from0.005 to 0.1 percent, preferably 0.01 to 0.05 percent.

Trichloroethylene stabilized with an acetylenic alcohol and a pyrroleaccording to the invention undergoes little or no decomposition ortendency to become acidic on storage in metal containers. It likewiseshows very little tendency to attack metals, even when thetrichloroethylene is at the boiling point and the metal is iron,aluminum, or any of the common aluminum-base alloys. In addition, theinhibitor mixture is largely effective in preventing attack of metal bythe condensing vapors of stabilized trichloroethylene, as in a vapordegreaser. Moreover, the inhibiting effect is not lost as thetrichloroethylene evaporates, the unevaporated residue being stillstabilized. Likewise, trichloroethylene is stabilized by the inhibitormixtures of the invention even when mixed with other chlorohydrocarbonsor other diluents which may be added.

It has been observed, however, that trichloroethylene stabilized with anacetylenic alcohol and a pyrrole, when stored over periods of severalmonths in ordinary black iron drums, occasionally tends to developdiscoloration. Such discoloration, attributable at least in part to thepresence of the pyrrole, is of no moment for many uses of thetrichloroethylene. However, the discoloration may be minimized or eveneliminated, and the stabilized trichloroethylene maintained clear, bydissolving therein a small proportion of an organic nitrogen base havinga substantial vapor pressure at the boiling temperature oftrichloroethylene. This base appears to restrain any tendency of thepyrrole component to cause discoloration, and may also contributesomething toward the stability of the trichloroethylene itself. Any of awide range of organic nitrogen bases may be used, although in general alower aliphatic amine, i. e. a monoamino hydrocarbon having no more thansix carbon atoms per molecule, is preferred, e. g. n-propyl amine,n-butyl amine, isopropyl amine, diisopropyl amine, etc. Diisopropylamine has proved extraordinarily effective, even in minute proportions.The proportion of diisopropyl amine or other nitrogen base required isin general from 0.0005 to 0.1 percent, with 0.0005 to 0.01 percentusually being pre ferred.

For most purposes, the inhibiting agents according to the invention areindividually dissolved in the proper amounts in the trichloroethylenesoon after it is manufactured. However, it is entirely feasible to makeup separately a concentrate consisting essentially of the acetylenicalcohol, the pyrrole, and optionally also the organic base, inappropriate relative proportions, and then add this concentrate to thetrichloroethylene, either at once or at some later time when severeexposure is expected. Such a concentrate may also be used to replenishthe inhibitor in a stabilized trichloroethylene which may show signs ofincipient instability due to long use or storage.

The following examples will illustrate the invention.

Example 1 To evaluate the effectiveness of various additives asinhibitors for the decomposition of trichloroethylene, an acceleratedlaboratory test was established. In each test, a 200 ml. sample of thetrichloroethylene composition and 10 ml. of water were introduced into aglass flask fitted with a long reflux condenser. Five gram portions ofiron, copper, zinc, and aluminum, each in the form of coarse powder,were also placed in the flask. In addition, strips of each metal insheet form were placed in the condenser in position to contact vapor andrefluxing liquid. The whole was then heated at a reflux temperature withvigorous boiling for a period of six Patented Aug. 20, 1957,

days. The acidity of the trichloroethylene, expressed as parts permillion, and the concentration of inorganic chloride, in parts permillion Cl, were determined by titration at the start and at the end ofeach test. 7

A s a blank determination, a sample of industrial gradetrichloroethylene (containing about 0.15 percent carbon tetrachloride asthe major chlorohydrocarbon impurity) and containing no inhibitor wassubjected to the test. Before the test the acidity was 230 p. p. m., andthe chloride about 2 p. p. m. At the end of the test, the acidity was494 p. p. m., and the chloride was 675 p. p. m. In a test according tothe invention, there were added to the same sample of trichloroethylcne0.1 percent of propargyl. alcohol, 0.05 percent of pyrrole, and 0.0015percent diisopropylamine'. Before the test, the material was slightlyalkaline (7 p. p. nu). After the test, the acidity was 93 p. p. m., andthe chloride was 149 p. p. m. It. will thus be seen that even under theextreme conditions of the test the decomposition of the stabilizedtrichloroethylene was only a small fraction of that of the uninhibitedmaterial.

The addition of 0.1 percent of dioxane to the com position of theinvention as an additional stabilizer did not appreciably affect theresults.

When the pyrrole was omitted, but the propargyl alcohol retained, thedegree of inhibition during the test was small.

Example 2 The test of of Example 1 was repeated using 0.05 percentpropargyl alcohol and 0.025 percent pyrrole. The results were virtuallyidentical with those in that example.

In a further test, using 0.1 percent propargyl alcohol, 0.025 percentpyrrole, and 0.0015 percent diisopropylamine, at the end of the six daysthe acidity of the stabilized trichloroethylene was 86 p. p. m. and thechloride was 123 p. p. m.

The stabilizing compositions of the invention are broadly effective instabilizing trichloroethylene from various sources. In the past,trichloroethylene made by the alkali dehydrochlorination of the productof the chlorination of acetylene has presented a dilferent stabilizationproblem from that of trichloroethylene made by highpyrrole.

2. A composition of matter, consisting essentially of trichloroethylenehaving dissolved. therein propargyl alcohol, pyrrole, and an organicnitrogenbase having a substantial vapor pressure at the boilingtemperature of trichloroethylene in a minor proportion sufiicient toinhibit decomposition of the trichloroethylene when in contact withmetal.

3. Trichloroethylene stabilized with from 0.005 to 1.0 percent ofpropargyl alcohol, from 0.005 to 0.1 percent pyrrole, and from 0.0005 to0.1 percent of a lower aliphatic amine.

4. Trichloroethylene stabilized with from 0.05 to 0.5 percent ofpropargyl alcohol, from 0.01 to 0.05 percent pyrrole, and 0.0005 to 0.01percent diisopropyl amine.

' 5. A method of inhibiting the decomposition of trichloroethyleneduring contact with one of the metals aluminum and iron which comprisesmaintaining dissolved therein from 0.005 to 1.0 percent of propargylalcohol and from 0.005 to 0.1 percent pyrrole.

References Cited in the file of this patent

1. TRICHLOROETHYLENE CONTAINING FROM 0.005 TO 1.0 PERCENT OF PROPARGYLALCOHOL AND FROM 0.005 TO 091 PERCENT PYRROLE.